Observation or measurement of peak voltage levels is often useful in electronic systems. In certain applications, the peak voltage of the AC signals to be measured can be quite large. For example, in a system that controls or observes residential power, the peak voltage can be 110-130 Volts AC, or 220-240 Volts AC.
The maximum AC voltage that can be safely received at an input pin for most current semiconductor integrated circuits is much lower than the peak voltage of many AC signals. Advanced analog integrated circuits that are currently commercially available from Texas Instruments Incorporated can have a maximum input rating of about 30-40 Volts. Direct coupling of the high voltage AC voltage signals to an input pin is therefore not possible using these modern analog integrated circuits.
In many applications, information about the peak voltage of an AC signal is needed, but it is not always necessary to get precise voltage value measurements. For example, if the application requires a “power good” indication of an AC power signal, a threshold measurement can be sufficient. In one application, if the threshold exceeds 110 Volts, it can be assumed the AC power is sufficiently good for system operations to begin or to continue. Other threshold voltages can be used for different applications.
An example is a so-called “smart” AC outlet which includes an indicator visible to a user. In an example, when the power is approximately 110-120 Volts, a green LED is enabled to visually signal the power is safe for use. When the power is not within a normal range, no green LED signal is enabled, or alternatively a red LED is enabled that can indicate a power problem to the user, indicating that the outlet is not safe to use. An exact numerical value of the AC voltage is not needed for this and many other “power good” applications.
Conventional circuitry arranged to observe an AC signal with a peak voltage above 30 Volts, for example, often requires an AC rectifier along with additional circuitry. In some conventional solutions special high voltage circuit components receive the high voltage AC signal. In alternative conventional solutions, a resistor divider receives the rectified AC signal and provides a divided output voltage that is proportional to the peak voltage (but which falls below a safe input voltage for the measurement circuitry). In addition, an analog to digital (ADC) converter circuit may be needed along with sampling logic to provide an output that indicates the peak voltage level. These ADC circuits are expensive, require precision circuitry and require circuit board area, which is undesirable. Further the resistors in a resistor divider are subject to temperature dependent value variations, and so a resistor divider measurement scheme may require expensive resistors and/or the use of additional temperature compensation circuitry to ensure proper operation of the circuit over a range of expected conditions.